Refer to the exhibit. Which configuration must be applied to each of the four routers on the network to reduce LDP LIB size and advertise label bindings for the /32 loopback IP space only? A. B. C. D.
if you actually read the document it is C
reating a Prefix List for MPLS LDP Local Label Allocation Filtering
Perform the following task to create a prefix list for LDP local label allocation filtering. A prefix list allows LDP to selectively allocate local labels for a subset of the routes learned from the IGP. The decrease in the number of local labels in the LDP LIB and the number of label mapping advertisements reduces the amount of memory use and improves convergence time for LDP.
SUMMARY STEPS
1. enable
2. configure terminal
3. ip prefix-list {list-name | list-number} [seq number] {deny network/length | permit network/length} [ge ge-length] [le le-length]
4. end
https://www.cisco.com/c/en/us/td/docs/ios/mpls/configuration/guide/convert/mp_ldp_book/mp_ldp_alloc_filter.html
wow! I'm DUMB IF I ACTUALLY PROOFREAD MY OWN POSTS!!!
I meant the answer is D.
first, you create the IP prefix then you move on to the next command shown on D
the correct answer is C
the prefix-list is not correct it must configured with ge not le
ip prefix-list LOOBACKS seq 5 permit 0.0.0.0/0 ge 32 or ( ge 32 le 32) in this case ,C and D will be correct
Answer: C
R3#sh run | s mpls
mpls ldp label
allocate global host-routes
no mpls ldp advertise-labels
R3#show mpls ldp bindings
lib entry: 10.0.12.0/24, rev 31
no local binding
lib entry: 10.0.23.0/24, rev 32
no local binding
lib entry: 10.0.24.0/24, rev 33
no local binding
lib entry: 172.16.0.1/32, rev 27
local binding: label: 20
lib entry: 172.16.0.2/32, rev 28
local binding: label: 16
lib entry: 172.16.0.3/32, rev 29
local binding: label: imp-null
lib entry: 172.16.0.4/32, rev 30
local binding: label: 19
allocate global host-routes:
This command instructs LDP to allocate local labels only for routes originating from IGP (Interior Gateway Protocol) that are host routes (prefixes with a /32 mask). In other words, labels will be assigned only for routes pointing to individual devices, not entire networks.
C is correct.
Perform the following task to configure LDP local allocation filtering. Configuring filtering policies for selective local label binding assignments by LDP improves LDP scalability and convergence. You can configure either a prefix list or host routes as a filter for local label allocation. A maximum of one local label allocation filter is supported for the global table.
Configures local label allocation filters for learned routes for MPLS LDP.
•The global keyword specifies the global routing.
•The host-routes keyword specifies that local label allocation be done for host routes only.
Answer is C
"Local label allocation filtering reduces the number of local labels allocated and therefore the number of messages exchanged with peers. This improves LDP scalability and convergence."
And how do we configure this?
https://www.cisco.com/c/en/us/td/docs/ios/mpls/configuration/guide/convert/mp_ldp_book/mp_ldp_alloc_filter.html#:~:text=privileged%20EXEC%20mode.-,Configuring%20MPLS%20LDP%20Local%20Label%20Allocation%20Filtering,-Perform%20the%20following
It should be C and not A because of the fact it should reduce the LIB size as well and this is not done only with C. A does regulate what is advertised but still has label assignments for all prefixes in the GRIB.
Correct answer is A.
1st. allocate bla bla doesn't exist.
2nd.
R2#show run | i ldp
no mpls ldp advertise-labels
mpls ldp advertise-labels for 30 to 20
R2#show ip access-lists
Standard IP access list 10
10 permit 10.10.24.4
Standard IP access list 20
10 permit 10.0.0.4 (3 matches)
Standard IP access list 30
10 permit 10.0.0.1 (6 matches)
R4#show mpls forwarding-table
Local Outgoing Prefix Bytes Label Outgoing Next Hop
Label Label or Tunnel Id Switched interface
16 No Label 10.0.0.3/32 0 Et0/0 10.10.24.2
17 No Label 10.0.0.2/32 0 Et0/0 10.10.24.2
18 17 10.0.0.1/32 0 Et0/0 10.10.24.2
19 No Label 10.10.23.0/24 0 Et0/0 10.10.24.2
20 No Label 10.10.12.0/24 0 Et0/0 10.10.24.2
If you tried to look for "allocate" at the global level, it's not there. It should've been indented. You have to enter "mpls ldp label" first, and then "allocate bla bla".
"allocate global host-routes": Configures local label allocation filters for learned routes for LDP.
The global keyword specifies the global routing.
The host-routes keyword specifies that local label allocation be done for host routes only.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_ldp/configuration/15-s/mp-ldp-15-s-book/mp-ldp-alloc-filter.html
Definitely C.
To prevent the distribution of any locally assigned labels, use the no advertise-labels command with no optional parameters. To reenable the distribution of all locally assigned labels to all LDP neighbors, use the advertise-labels command with no optional parameters.
For that reason, A and B are not correct, the answer is C
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